whats is difference between Java JRE and Java SDK

Hi, what is the difference between Java JRE and Java SDK... i think both of them have the same set of files to be installed... I am not able to understand where they differ
[200 byte] By [HelloTamilaa] at [2007-10-1 1:14:10]
# 1
The JRE (Java runtime Environment) contains just the stuff necessary to run Java and the SDK (System Development Kit) contains the extra stuff necessary (and also helpful) to develop in Java.
bbrittaa at 2007-7-8 1:30:30 > top of Java-index,Security,Event Handling...
# 2
jre does not contain javac.exe(the external java compiler) so yopu can not compile your source code
Raj_2005a at 2007-7-8 1:30:30 > top of Java-index,Security,Event Handling...